With the development of digital technologies regarding electronic devices, in order to store data such as images, requirements arise for a larger capacity of nonvolatile variable resistance elements, reduction of power consumption for writing, a higher speed for a writing/reading time, a longer duration, and the like. It is considered that current attempt at more microfabricated flash memories using floating gates has a limit to satisfy such requirements.
One conventional technology having a possibility of satisfying the requirements is disclosed to provide a nonvolatile variable resistance element made of a perovskite material (for example, Pr(1−x)CaxMnO3[PCMO], LaSrMnO3[LSMO], GdBaCoXOY[GBCO], and the like) (refer to Patent Reference 1). In this technology, the perovskite material receives electric pulses (voltages having waveforms with short durations) having different polarities in order to increase or decrease a resistance value of the material, which enables the nonvolatile variable resistance element to memorize data in association with the varying resistance value.
There is another conventional technology for switching a resistance value by using electric pulses having the same polarity. In the technology, a nonvolatile variable resistance element exploits the characteristics that a resistance value of a film made of a transition metal oxide (NiO, V2O, ZnO, Nb2O5, TiO2, WO3, or CoO) is varied when electric pulses having different pulse widths are applied to the film (refer to Patent Reference 2). There is also a variable resistance element made of a transition metal oxide film in a structure of a crosspoint memory array using diodes.    [Patent Reference 1] U.S. Pat. No. 6,204,139, Specification    [Patent Reference 2] Japanese Unexamined Patent Application Publication No. 2004-363604